1. Field of the Invention
The present invention relates to a method for adjusting the profile of a continuously cast slab, particularly of a thin slab, wherein the profile is determined in accordance with given requirements with respect to its camber or wedge shape (conicity) by the gap geometry of strand guide rollers of the guide segments of a strand guiding system.
The invention also relates to an apparatus for carrying out the method.
2. Description of the Related Art
Increased requirements are made of the slab profile and especially the thin slab profile of a casting machine with respect to the camber or the wedge shape in order to produce the required profile tolerances, particularly in the case of small final rolling thicknesses.
The slab profile is essentially dependent on the roll gap geometry in the area of the residual solidification of the strand. Alignment errors, roll wear, elastic deformations of the segment, temperature influences and different casting widths, as well as a different solidification profile over the casting length and width, result in a roll gap geometry and, thus, a casting profile which partially does not meet the high requirements of the rolling mill and, thus, of the end product.
These relationships and reasons are known in the art. DE 197 45 056 discloses a method of producing slabs in a continuous casting plant with a strand guiding system divided into segments and arranged following a casting mold, composed of a two-part segment frame whose frame parts are clamped together by means of hydraulic cylinders, wherein pairs of oppositely located rollers are mounted in the frame parts for supporting and for conveying the solidifying cast strand, and wherein at least one of these rollers, i.e., the drive roller, is adjusted for transmitting the strand conveying forces with a defined adjusting force relative to the cast strand, such that the clamping of the segment frame parts takes place steplessly by position-controlled and force-controlled segment adjusting cylinders which also apply the adjusting force for the drive roller required for transmitting the strand conveying forces.
A continuous casting plant for carrying out the method for producing slabs contains four position-controlled and force-controlled segment adjusting cylinders which connect the two segment frame parts at a distance without spacers and clamp the segment frame parts relative to each other.
DE 43 06 853 A1 describes a strand guiding system in continuous casting plants for producing slabs, particularly in accordance with the casting and rolling method, with rollers which are arranged in pairs opposite each other and can be adjusted to different strand thicknesses, wherein the rollers are mounted at frames or stand parts of the strand guiding system connected through tension rods, and wherein the tension rods are formed by piston/cylinder units and spacer pieces are placed in the flux of the force of the piston/cylinder units between upper and lower frame parts. Arranged between the spacer piece and the cylinder of the piston/cylinder unit is an annular hydraulic cylinder which surrounds the piston rod and whose annular piston supports with frictional engagement the spacer piece. The annular hydraulic cylinders are supported on side frames and the side frames connect at least two lower frames to a segment of the strand guiding system.
EP 0 545 104 B1 discloses a method of continuously casting slabs or blooms in a continuous casting plant with a soft reduction section which includes rollers which can be adjusted individually or as a segment relative to each other by means of hydraulic cylinders, wherein the clear distance between the rollers is steplessly adjustable by means of spindles. The adjusting force during casting is reduced and the spindles are adjusted under reduced load to a desired opening width. For this purpose, it is proposed to continuously measure the difference between cylinder force and ferrostatic load. In an apparatus for carrying out the method in a continuous casting plant with soft reduction section, which includes rollers which can be adjusted individually or as a segment by means of hydraulic cylinders relative to each other and in which the clear distance between the rollers can be adjusted steplessly, the spindles are supported on pressure cells which continuously measure the adjusting force and are connected to an adjusting drive.
In the prior art discussed above, those skilled in the art cannot find any suggestions in what manner or with what means it might be possible to meet the concrete requirements with respect to the camber and the wedge shape of slab profiles, or how in the case of small final rolling thicknesses the profile tolerances required in that case can be produced or maintained.
Starting from the prior art discussed above, it is the primary object of the present invention to propose a novel strand guiding concept which, in addition to being less expensive, makes it possible to influence in a targeted manner the camber and wedge shape of a slab profile, particularly of a thin slab profile.
In accordance with the present invention, taking into consideration the known fact that the slab profile is dependent substantially on the roll gap geometry in the area of the residual solidification of the strand, the above object is met by determining the adjustment of the strand guide rollers at least in the area of the residual solidification and the adjusting forces of adjusting means required for this purpose in such a way that a predeterminable desired value for the slab profile can be adjusted for any characteristic state of operation.
The computation can be carried out by means of on-line process models. The adjustment of the rollers to a roller gap geometry in the area of the residual solidification of the strand which can be achieved in accordance with the present invention makes it possible in an optimum manner to meet the predetermined requirements with respect to camber and wedge shape of a slab profile. Also compensated by the method are alignment errors, roller wear, elastic deformations of the segment due to ferrostatic loads and the temperature influence as well as different casting widths.
In accordance with a further development of the method, the determination of the desired values is carried out by way of previous computation for the preadjustment of the strand guide rollers as well as on-line during operation for the on-line adjustment of the rollers.
In accordance with the invention, desired values can be preset in dependence on different operational loads, in dependence on different slab dimensions, in dependence on different steel qualities, or in dependence on different casting speeds and casting temperatures.
The desired values are preferably preset in dependence on different plant conditions, such as state of alignment, state of wear and/or state of thermal expansion, wherein the desired values are preferably preset in accordance with at least two characteristic states of operation.
The method according to the invention is especially characterized in that adjusting forces act on a guide segment on one side, either the loose side or the fixed side, preferably on the fixed side, wherein the adjusting forces influence in a targeted manner in the middle area the deformation of the segment for achieving a desired slab profile.
In the apparatus for adjusting the slab profile of a continuously cast slab, particularly of a thin slab, wherein the profile is determined in accordance with given requirements with respect to its camber and/or wedge shape by the gap geometry of strand guide rollers of a strand guiding system, and wherein the rollers are mounted in individual strand guide segments and in pairs opposite each other on frame parts which form a fixed side and a loose side and are clamped together by adjusting means through tension rods at their outer end portions, the invention provides that at least one force application means is arranged in the middle portion of the frame parts, wherein the force application means is configured to apply tensile forces as well as compressive forces.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.